Applications In Nano-optics Research Articles

"Sketch and Peel" Lithography for High-Resolution Multiscale Patterning.

We report a unique lithographic process, termed "Sketch and Peel" lithography (SPL), for fast, clean, and reliable patterning of metallic structures from tens of nanometers to submillimeter scale using direct writing technology. The key idea of SPL process is to define structures using their presketched outlines as the templates for subsequent selective peeling of evaporated metallic layer. With reduced exposure area, SPL process enables significantly improved patterning efficiency up to hundreds of times higher and greatly mitigated proximity effect compared to current direct writing strategy. We demonstrate that multiscale hierarchical metallic structures with arbitrary shapes and minimal feature size of ∼15 nm could be defined with high fidelity using SPL process for potential nanoelectronic and nano-optical applications.

Far-field radially polarized focal spot from plasmonic spiral structure combined with central aperture antenna.

Manipulation of a vector micro-beam with an optical antenna has significant potentials for nano-optical technology applications including bio-optics, optical fabrication, and quantum information processing. We have designed and demonstrated a central aperture antenna within an Archimedean spiral that extracts the bonding plasmonic field from a surface to produce a new vector focal spot in far-field. The properties of this vector focal field are revealed by confocal microscopy and theoretical simulations. The pattern, polarization and phase of the focal field are determined by the incident light and by the chirality of the Archimedean spiral. For incident light with right-handed circular polarization, the left-handed spiral (one-order chirality) outputs a micro-radially polarized focal field. Our results reveal the relationship between the near-field and far-field distributions of the plasmonic spiral structure, and the structure has the potential to lead to advances in diverse applications such as plasmonic lenses, near-field angular momentum detection, and optical tweezers.

Shaping the nonlinear near field.

Light scattering at plasmonic nanoparticles and their assemblies has led to a wealth of applications in metamaterials and nano-optics. Although shaping of fields around nanostructures is widely studied, the influence of the field inside the nanostructures is often overlooked. The linear field distribution inside the structure taken to the third power causes third-harmonic generation, a nonlinear optical response of matter. Here we demonstrate by a far field Fourier imaging method how this simple fact can be used to shape complex fields around a single particle alone. We employ this scheme to switch the third-harmonic emission from a single point source to two spatially separated but coherent sources, as in Young's double-slit assembly. We envision applications as diverse as coherently feeding antenna arrays and optical spectroscopy of spatially extended electronic states.

From transverse angular momentum to photonic wheels

This Progress Article details the latest achievements and underlying principles of light carrying transverse spin.The capabilities and future applications of this young yet already advanced field are highlighted. Scientists have known for more than a century that light possesses both linear and angular momenta along the direction of propagation. However, only recent advances in optics have led to the notion of spinning electromagnetic fields capable of carrying angular momenta transverse to the direction of motion. Such fields enable numerous applications in nano-optics, biosensing and near-field microscopy, including three-dimensional control over atoms, molecules and nanostructures, and allowing for the realization of chiral nanophotonic interfaces and plasmonic devices. Here, we report on recent developments of optics with light carrying transverse spin. We present both the underlying principles and the latest achievements, and also highlight new capabilities and future applications emerging from this young yet already advanced field of research.

High‐Performance Broadband Circularly Polarized Beam Deflector by Mirror Effect of Multinanorod Metasurfaces

Manipulation of light phase and amplitude by plasmonic metasurfaces has immensely promising applications in optical imaging, information processing, communications, and quantum optics. However, the controllability of efficiency and bandwidth is relatively low for the single‐layer metasurfaces. Here, a high efficiency and broadband circularly polarized (CP) beam deflector based on multirod single‐layer metasurfaces is presented. Each unit can be regarded as an imperfect polarizer, and the phase and amplitude induced by the mirror effect can be easily controlled. Owing to the plasmonic hybridization, the high efficiency and broadband characteristics of the proposed metasurfaces are theoretically and experimentally demonstrated. Meanwhile, an easy way to determine the polarization degree of the incident light based on Poincaré sphere is also proved by the multirod metasurfaces. Our work provides a simple alternative way to enhance the efficiency of CP anomalous light and thus has robust applications in nanophotonics and nanooptics.

Laser trapping of colloidal metal nanoparticles.

Optical trapping using focused laser beams (laser tweezers) has been proven to be extremely useful for contactless manipulation of a variety of small objects, including biological cells, organelles within cells, and a wide range of other dielectric micro- and nano-objects. Colloidal metal nanoparticles have drawn increasing attention in the field of optical trapping because of their unique interactions with electromagnetic radiation, caused by surface plasmon resonance effects, enabling a large number of nano-optical applications of high current interest. Here we try to give a comprehensive overview of the field of laser trapping and manipulation of metal nanoparticles based on results reported in the recent literature. We also discuss and describe the fundamentals of optical forces in the context of plasmonic nanoparticles, including effects of polarization, optical angular momentum, and laser heating effects, as well as the various techniques that have been used to trap and manipulate metal nanoparticles. We conclude by suggesting possible directions for future research.

Fabrication of aluminium nanostructures for plasmonics

Metallic nanostructures are the building blocks for nanoplasmonics and for subsequent applications in nanooptics. For several decades, plasmonics have been almost exclusively studied in the visible region by using nanostructures made of noble metals exhibiting plasmonic properties in the near infrared to visible range. This notwithstanding, emerging applications will require the extension of nanoplasmonics toward higher energies, particularly in the UV range. Therefore, alternative metals, often described as poor metals are emerging to achieve that goal. Among all these metals, aluminium appears to be one of the most appealing for extending plasmonics towards ultraviolet energies. Aluminium is cheap, widely available, compatible with optoelectronic devices and exhibits plasmonic properties over a wide range of energies, from the infrared to the deep UV. Our aim is to present a review of current research centred on the fabrication of aluminium nanostructures. Mastering the geometry of aluminium nanostructures is extremely important in order to tune their plasmonic properties and target a given application. First we give an introduction to the nanofabrication of aluminium nanostructures within the context of plasmonics. The review then focuses on the possible geometries that such structures may take when fabricated with specific fabrication techniques. Each technique is detailed and the plasmonic properties of the aluminium nanostructures are briefly described. When possible, an example of an application is given. Finally, the future applications of aluminium plasmonics are highlighted and a conclusion with perspectives is given.

Hole-mask colloidal nanolithography combined with tilted-angle-rotation evaporation: A versatile method for fabrication of low-cost and large-area complex plasmonic nanostructures and metamaterials

Many nano-optical applications require a suitable nanofabrication technology. Hole-mask colloidal nanolithography has proven to be a low-cost and large-area alternative for the fabrication of complex plasmonic nanostructures as well as metamaterials. In this paper, we describe the fabrication process step by step. We manufacture a variety of different plasmonic structures ranging from simple nano-antennas over complex chiral structures to stacked composite materials for applications such as sensing. Additionally, we give details on the control of the nanostructure lateral density which allows for the multilayer-fabrication of complex nanostructures. In two accompanying movies, the fabrication strategy is explained and details are being demonstrated in the lab. The movies can be found at the website of Beilstein TV.

Violet-green excitation for NIR luminescence of Yb3+ ions in Bi2O3-B2O3-SiO2-Ga2O3 glasses.

60Bi(2)O(3)-20B(2)O(3)-10SiO(2)-10Ga(2)O(3) glasses doped with 1-9 mol% Yb(2)O(3) were prepared and investigated mainly on their violet-green excitation for the typical NIR emission of Yb(3+), generally excited in the NIR. Two violet excitation bands at 365 nm and 405 nm are related to Yb(2+) and Bi(3+). 465 nm excitation band and 480 nm absorption band in the blue-green are assigned to Bi(0) metal nanoparticles/grains. Yb-content-dependence of the excitation and absorption means that Bi(0) is the reduced product of Bi(3+), but greatly competed by the redox reaction of Yb(2+) ↔ Yb(3+). It is proved that the violet-green excitations result in the NIR emission of Yb(3+). On the energy transfer, the virtual level of Yb(3+)-Yb(3+) as well as Bi(0) dimers probably plays an important role. An effective and controllable way is suggested to achieve nano-optical applications by Bi(0) metal nanoparticles/grains and Yb(3+).

Ab initiosimulations of light propagation in silver cluster nanostructures

We present a theoretical approach for the simulation of the optical response and light propagation in aggregates and in ordered arrays of small noble-metal clusters with discrete electronic structure. We construct the Hamiltonian for the aggregate system based on the time-dependent density functional theory electronic states of the individual subunits and describe the interaction between them using the dipole approximation. The time evolution of the aggregate under the influence of the external electric field is obtained from the numerical solution of the time-dependent Schr\odinger equation with the coupled excitonic Hamiltonian. For each subunit, the time-dependent dipole moment is calculated using the reduced density matrix formalism. Such quantum-mechanically determined dipole moments are used to simulate the spatiotemporal distribution of the electric field produced by the array. Additionally, we introduce an approximate self-consistent iterative approach to treat arrays consisting of many subunits which are of interest in the context of nanoplasmonics, nano-optical applications, and development of light-harvesting materials. The developed methodology is illustrated first on the example of Ag${}_{2}$ and Ag${}_{8}$ cluster pairs. Subsequently, light propagation in a triangular-shaped array consisting of six Ag${}_{8}$ clusters is simulated.

Nanosphere Lithography: Parallel Fabrication of Plasmonic Nanocone Sensing Arrays (Small 23/2013)

Ordered arrays of nanocones and nanopyramids are fabricated in a fully parallel approach by M. Fleischer and co-workers, as reported on page 3987. Single or double layers of self-assembled nanospheres are directly modified or used as templates for the creation of etch masks. Nanocones with sharp tips form when the masks are transferred into a gold or silver layer. Under optical excitation, narrowly confi ned hotspots are created near the cone tips. These structures have interesting properties for nano-optical applications and are evaluated as substrates for surface enhanced Raman spectroscopy using a thin film of pentacene molecules.

A self-assembled three-dimensional cloak in the visible.

An invisibility cloak has been designed, realized and characterized. The cloak hides free-standing sub-wavelength three-dimensional objects at the short wavelength edge of the visible spectrum. By a bottom-up approach the cloak was self-assembled around the object. Such fabrication approach constitutes a further important step towards real world applications of cloaking; leaving the realm of curiosity. The cloak and the way it was fabricated opens an avenue for many spectacular nanooptical applications such as non-disturbing sensors and photo-detectors, highly efficient solar cells, or optical nanoantenna arrays with strongly suppressed cross-talk to mention only a few. Our results rely on the successful combination of concepts from various disciplines, i.e. chemistry, material science, and plasmonics. Consequently, this work will stimulate these fields by unraveling new paths for future research.

Time-Resolved Energy-Momentum Spectroscopy of Electric and Magnetic Dipole Transitions in Cr3+:MgO

Due to the recent interest in magnetic light-matter interactions, the magnetic dipole (MD) transitions in lanthanide ions have been studied for potential applications in nano-optics. Similar to lanthanide ions, transition-metal ions also exhibit strong MD emission at room temperature, but their prominent MD zero-phonon lines are often accompanied by significant electric dipole (ED) sideband emission. Here, we extend energy-momentum spectroscopy to time-resolved measurements, and use this technique to quantify the ED and MD contributions to light emission from trivalent chromium doped magnesium oxide (Cr(3+):MgO). This allows us to differentiate the MD (2)E → (4)A2 zero-phonon line from phonon-assisted (2)E → (4)A2 and (4)T2 → (4)A2 ED sidebands. We also demonstrate how the relative intensities of the sharp MD zero-phonon line and the broad ED sidebands can be used as a qualitative measure of the MD and ED local density of optical states.

Enhanced Second Harmonic Generation by Photonic–Plasmonic Fano-Type Coupling in Nanoplasmonic Arrays

In this communication, we systematically investigate the effects of Fano-type coupling between long-range photonic resonances and localized surface plasmons on the second harmonic generation from periodic arrays of Au nanoparticles arranged in monomer and dimer geometries. Specifically, by scanning the wavelength of an ultrafast tunable pump laser over a large range, we measure the second harmonic excitation spectra of these arrays and demonstrate their tunability with particle size and separation. Moreover, through a comparison with linear optical transmission spectra, which feature asymmetric Fano-type lineshapes, we demonstrate that the second harmonic generation is enhanced when coupled photonic-plasmonic resonances of the arrays are excited at the fundamental pump wavelength, thus boosting the intensity of the electromagnetic near-fields. Our experimental results, which are supported by numerical simulations of linear optical transmission and near-field enhancement spectra based on the Finite Difference Time Domain method, demonstrate a direct correlation between the onset of Fano-type coupling and the enhancement of second harmonic generation in arrays of Au nanoparticles. Our findings enable the engineering of the nonlinear optical response of Fano-type coupled nanoparticle arrays that are relevant to a number of device applications in nonlinear nano-optics and plasmonics, such as on-chip frequency generators, modulators, switchers, and sensors.

Plasmonic near-field probes: a comparison of the campanile geometry with other sharp tips

Efficient conversion of photonic to plasmonic energy is important for nano-optical applications, particularly imaging and spectroscopy. Recently a new generation of photonic/plasmonic transducers, the 'campanile' probes, has been developed that overcomes many shortcomings of previous near-field probes by efficiently merging broadband field enhancement with bidirectional coupling of far- to near-field electromagnetic modes. In this work we compare the properties of the campanile structure with those of current NSOM tips using finite element simulations. Field confinement, enhancement, and polarization near the apex of the probe are evaluated relative to local fields created by conical tapered tips in vacuum and in tip-substrate gap mode. We show that the campanile design has similar field enhancement and bandwidth capabilities as those of ultra-sharp metallized tips, but without the substrate and sample restrictions inherent in the tip-surface gap mode operation often required by those tips. In addition, we show for the first time that this campanile probe structure also significantly enhances the radiative rate of any dipole emitter located near the probe apex, quantifying the enhanced decay rate and demonstrating that over 90% of the light radiated by the emitter is "captured" by this probe. This is equivalent to collecting the light from a solid angle of ~3.6 pi. These advantages are crucial for performing techniques such as Raman and IR spectroscopy, white-light nano-ellipsometry and ultrafast pump-probe studies at the nanoscale.

Rainbow Radiating Single-Crystal Ag Nanowire Nanoantenna

Optical antennas interface an object with optical radiation and boost the absorption and emission of light by the objects through the antenna modes. It has been much desired to enhance both excitation and emission processes of the quantum emitters as well as to interface multiwavelength channels for many nano-optical applications. Here we report the experimental implementation of an optical antenna operating in the full visible range via surface plasmon currents induced in a defect-free single-crystalline Ag nanowire (NW). With its atomically flat surface, the long Ag NW reliably establishes multiple plasmonic resonances and produces a unique rainbow antenna radiation in the Fresnel region. Detailed antenna radiation properties, such as radiating near-field patterns and polarization states, were experimentally examined and precisely analyzed by numerical simulations and antenna theory. The multiresonant Ag NW nanoantenna will find superb applications in nano-optical spectroscopy, high-resolution nanoimaging, photovoltaics, and nonlinear signal conversion.

Magnetic plasmon in coupled nanosandwich structure

We investigate the magnetic resonant modes in the coupled nanosandwich (CSW) structure, which can be considered a metamolecule composed of two meta-atoms (nanosandwiches). The coupling between two nanosandwiches leads to two magnetic resonant modes, the split of the single magnetic resonant mode. Moreover, the coupling effect in a more complicated system that consists of two closely placed CSWs is studied, where four magnetic resonant modes with different phase relationships between meta-atoms are observed. It is shown that the interaction between CSWs leads to this secondary split of the magnetic resonant mode. We further consider a one-dimensional metacrystal formed by a chain of CSWs, and directly observe the magnetic plasmon (MP) bands through the Fourier transformation approach. Modifying both the thickness of the middle metal layer of CSWs and the spacing between CSWs, one can efficiently engineer the MP band, and even open a bandgap. Such a CSW chain can even work as a subwavelength waveguide, which may have potential applications in nano-optics and photonics.

Microwave-Assisted Synthesis of Shuttle-shaped Single-Crystalline Te Nanotubes Decorated with Spherical Particles

Shuttle-shaped single-crystalline Te nanotubes decorated with spherical particles on outer surface have been successfully synthesized in reaction media of polyol solvent through a simple and rapid microwave-assisted approach. The length, outer diameter and wall thickness of as-synthesized Te nanotubes were roughly measured at 5-15 μm, 300-500 nm and 100-150 nm, respectively. The crystal growth process of Te nanotubes was investigated and discussed as the key issue of this present study, and it was found that the scrollinggrowth- based mechanism would best account for the formation process of the shuttle-shaped Te nanotubes. Photoluminance (PL) measurements displayed that the as-synthesized Te nanotubes can not only give strong violet blue emission but also strong red emission, and such unique optical property could be beneficial for nano-optical applications. Keywords: Te nanotubes, microwave-assisted, polyol, photoluminance, Shuttle-shaped, Spherical Particles, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM)

Fabrication of metamaterials in the optical spectral range

Recently, the fabrication and optimization of nano-hole arrays in multi-layers has attracted much attention for their interesting applications in nano-optics and biosensing. In particular nano-hole arrays in metal-dielectric-metal stacks, also known as “fish-net” type structures, actually are the best candidates to accomplish some suggestive physical phenomena like negative refractive index, super-lensing and invisibility cloaks in the optical spectral range. Here, we report our preliminary results on the nanofabrication of “fish-net” type Au/dielectric/Au metamaterial stacks. Nano-hole arrays have been realized on Au (30nm)–dielectric (50nm)–Au (30nm)/ITO stacks by means of direct ion milling with FIB using a FEI Nova 600i instrument. Finite element method (FEM) simulations were used to design the structures and to foresee their optical behavior.

Extreme Scattering Effect: Light scattering analysis via the Discrete Sources Method

The effect of the Extraordinary Optical Transmission (Ebbesen et al. Nature 1998; 391, 667) through subwavelength holes array in noble metal screen is used for multiple practical applications in nanooptics and biophotonics. In this paper the Extreme Transmission Effect (Eremina et al. Opt. Comm. 2008; 281, 3581) in the noble metal film deposited on a glass prism in the evanescent wave’s area is in focus. The Discrete Sources Method (DSM) has been adjusted to calculate the polarized light scattering by an axially symmetric inclusion located in a film deposited on a glass prism. We extended the DSM for the evaluation of the Scattering Cross-Section in the prism domain. It has been shown that the maximum value of the Reflection Cross-Section appears at the same incident angle as for the Transmission Cross-Section. It has been demonstrated that the Reflection Cross-Section can exceed the Transmission Cross-Section under certain circumstances. Analysis of the correlation between the Plasmon Resonance in the gold film and the Extreme Scattering Effect demonstrates that the Plasmon Resonance plays an important but not the exclusive role in the appearance of the Extreme Scattering Effect.